Uroptychus marcosi, Baba, 2018

Baba, Keiji, 2018, Chirostylidae of the Western and Central Pacific: Uroptychus and a new genus (Crustacea: Decapoda: Anomura), Tropical Deep-Sea Benthos (Mémoires du Muséum national d'Histoire naturelle 212), pp. 1-612 : 301-304

Uroptychus marcosi n. sp.

Figures 141 , 142

TYPE MATERIAL — Holotype: New Caledonia, Chesterfield Islands . MUSORSTOM 5 Stn CC 365, 19°43’S, 158°48’E, 710 m, 19.X.1986, with corals of Isididae (Calcaxonia) , ♀ 7.2 mm ( MNHN-IU-2014-16725 ).

ETYMOLOGY„ The species is named for Marcos S. Tavares for his long-lasting friendship.

DISTRIBUTION„ Chesterfield Islands; 710 m.

DESCRIPTION — Medium-sized species. Carapace: 1.2 × longer than broad; greatest breadth 1.6 × distance between anterolateral spines. Dorsal surface smooth and glabrous, slightly convex from anterior to posterior, with feeble depression between gastric and cardiac regions. Lateral margins posteriorly divergent to point one-quarter from posterior end, then gently convex; ridged along posterior two-fifths of length; anterolateral spine small, ending in somewhat acuminate lateral limit of orbit. Rostrum narrowly triangular, with interior angle of 20°, nearly straight and horizontal, slightly overreaching cornea; length 0.4 × that of remaining carapace, breadth less than half carapace breadth at posterior carapace margin; dorsal surface flattish. Lateral limit of orbit without distinct spine, situated distinctly anterior to and well separated from anterolateral spine. Pterygostomian flap anteriorly angular, ending in very small spine; surface smooth.

Sternum: Excavated sternum subtriangular on anterior margin, surface with small spine in center. Sternal plastron slightly shorter than broad, lateral extremities divergent posteriorly. Sternite 3 shallowly depressed, anterior margin broadly and deeply excavated, with 2 small submedian spines (additional small spine lateral to right spine); anterolateral angle rounded. Sternite 4 with slightly convex anterolateral margin anteriorly ending in small spine followed by posteriorly diminishing eminences; posterolateral margin half as long as anterolateral margin. Anterolateral margin of sternite 5 convexly divergent posteriorly, about as long as posterolateral margin of sternite 4.

Abdomen: Smooth and glabrous. Somite 1 smooth on surface, moderately convex from anterior to posterior. Somite 2 tergite 2.3 × broader than long; pleuron posterolaterally blunt, lateral margins somewhat concave and strongly divergent posteriorly. Pleuron of somite 3 posterolaterally rounded. Telson slightly more than half as long as broad; posterior plate distinctly emarginate on posterior margin, length 1.5 × that of anterior plate.

Eye: Relatively broad (1.6 × longer than broad), falling short of apex of rostrum, slightly broadened distally, mesial margin somewhat concave, lateral margin convex. Cornea somewhat inflated, nearly as long as remaining eyestalk.

Antennule and antenna: Antennular ultimate article twice as long as high. Antennal peduncle terminating in corneal distal margin, relatively slender. Article 2 with small but distinct distolateral spine. Antennal scale ending in midlength of article 5, breadth about 2 × that of article 5. Distal 2 articles unarmed; article 5 2.3 × longer than article 4, breadth less than half height of antennular ultimate article. Flagellum of 15 segments barely reaching distal end of P1 merus.

Mxp: Mxp1 with bases close to each other. Mxp3 basis with 4 denticles on mesial ridge. Ischium with 12-14 denticles on proximal three-quarters of crista dentata, flexor margin distally not rounded. Merus elongate, 2.5 × longer than ischium; flexor margin ridged and unarmed; distolateral spine absent. Carpus also unarmed.

P1: Slender, 4.6 × longer than carapace. Ischium dorsally with moderate-sized, flattish spine, ventromesially with a few proximal spines and no subterminal spine. Merus with blunt low distomesial process ventrally, length slightly more than that of carapace. Carpus unarmed, 1.2 × longer than merus. Palm with subparallel mesial and lateral margins, 4.2 × longer than broad, finely granulate ventrally, length 0.8 × that of carpus. Fingers with relatively short setae as illustrated,

not distinctly crossing when closed, each distally ending in papilla-like small spine; movable finger half as long as palm, opposable margin with low proximal process fitting into longitudinal groove on opposite face of fixed finger when closed.

P2-4: Relatively slender, with sparse long setae. Meri well compressed mesio-laterally, unarmed, successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.7-0.8 × length of P3 merus), equally broad on P2-3, P4 merus 0.9 × as broad as P3 merus; length-breadth ratio, 5.4 on P2, 4.8 on P3, 4.1 on P4; P2 merus 0.9 × length of carapace, 1.2 × length of P2 propodus; P3 merus 1.1 × length of P3 propodus; P4 merus subequal to length of P4 propodus. Carpi slightly more than half length of propodi, much longer than dactyli (carpus-dactylus length ratio, 1.5 on P2, 1.4 on P3, 1.2 on P4); P3 carpus 0.9 × length of P2 carpus, P4 carpus 0.8 × length of P3 carpus. Propodi subequal in length on P2 and P3, shorter on P4; flexor margin straight, with row of 6 or 7 slender spines on P2, 4 or 5 spines on P3 and P4, distalmost single, located at point one-fourth from juncture with dactylus on P2, more remote on P3 and P4. Dactyli strongly curving at proximal third, shorter than carpi (dactylus-carpus length ratio, 0.7 on P2 and P3, 0.8 on P4), 0.4 × as long as propodi on P2-4; flexor margin with 10 spines, ultimate spine largest, penultimate more remote from antepenultimate than from ultimate on P2 and P3, remaining spines oriented parallel to flexor margin and diminishing toward base of article.

REMARKS — The new species resembles U. australis ( Henderson, 1885) in the shapes of the carapace and sternal plastron, and in the spination of P2-4 dactyli. However, they are readily distinguished by the following differences. In U. marcosi , the P4 merus is longer, being 0.7-0.8 instead of 0.5-0.6 times the length of P3 merus; the P2-4 propodi bear the distalmost of the flexor marginal spines single and noticeably remote from the juncture with the dactylus whereas the distalmost is paired with another spine mesial to it and very close to the juncture in U. australis ; the lateral limit of the orbit is angular, without spine instead of ending in a distinct spine, and the antennal scale terminates in the midlength of the antennal article 5, instead of reaching the distal end of that article.

Uroptychus marcosi also shares the following characters with U. bispinatus Baba, 1988 and U. vandamae Baba, 1988 : the carapace lateral margin bearing an anterolateral spine only; the P2-4 dactyli with the flexor spines oriented parallel to the margin; the P2-4 propodi with the terminal one of the flexor spines single, not paired; and the antennal scale short, terminating at most in the midlength of article 5. Uroptychus marcosi differs from U. bispinatus in having the posterolateral margin of sternite 4 distinctly shorter than instead of as long as the anterolateral margin, in having the pterygostomian flap anteriorly produced to a distinct spine instead of being roundish with a very small spine, in having the P2-4 propodi with 2 or 3 instead of 4 or 5 flexor marginal spines distant from the juncture with the dactyli, and in having the carapace distinctly longer than instead of as long as broad.

Uriptychus vandamae has a rostrum that extends far beyond the eyes; the anterolateral spine of the carapace is relatively strong; the terminal one of the flexor spines of P2-4 propodi is closer to the juncture with the dactyli and remote from the distal second spine; and the antepenultimate spine of P2-4 dactyli is noticeably distant from the penultimate ( Figure 275 ), all to mention the differences from U. marcosi .

Figures

FIGURE 141 Uroptychus marcosi n. sp., holotype, female 7.2 mm (MNHN-IU-2014-16725). A, carapace and anterior part of abdomen, dorsal. B, same, lateral.C, sternal plastron,with excavated sternum and basal parts of Mxp1. D, telson. E, left antenna,ventral.F, left Mxp3, setae omitted, ventral.G, same, lateral.H, left P1, dorsal.Scale bars:1 mm.

FIGURE 142 Uroptychus marcosi n. sp.,holotype,female 7.2 mm (MNHN-IU-2014-16725). A, right P2, lateral.B, same,distal part, setae omitted, lateral.C, right P3, setae omitted,lateral. D, right P4, lateral. E, same, distal part, lateral.Scale bars: 1 mm.

FIGURE 275 Uroptychus vandamae Baba,1988,ovigerous female 6.9 mm (MNHN-IU-2014-17010). A, carapace and anterior part of abdomen, lateral. B, anterior part of carapace, dorsal. C, sternal plastron, with excavated sternum and basal parts of Mxp1. D, right Mxp3, setae omitted, ventral. E, left P2, distal articles, setae omitted, lateral.F, same. G, right P4, distal articles, setae omitted, lateral. H, same. Scale bars: 1 mm.